Combining and separating circuits



Oct. 9, 1951 KENYQN 2,570,249

COMBINING AND SEPARATING CIRCUITS Filed March 29, 1947 2 Sheets-Sheet l INVENTOR. ,2) W0 5. lfzwvo/v flTTOR/VEY Oct. 9, 1951 D. E. KENYON COMBINING AND SEPARATING cmcuns 2 Sheets-Sheet 2 Filed March 29, 1947 Patented Oct. 9, 1951 I H [2,."si'id249 i COMBINING A'NnsErAnA'rINo o ncorrs f David E. i i enyoin, ColdS prIng Harbor, Y., --ias-- signor tol'lfhesperryf tion of Delaware,

Corporation, a corpora- "ApplicationMarch 29,-1947,Serial'No;738,055.41 as Llcularly to novel circuits whichare adapted to combine or mix and separate a pluralityof signal voltages in such a manner that precedence. may be given to a desired one of these signals.

The circuits of the present invention, although not limited to such use,-are especially adapted for use in combination with the 1-teledata system disclosed in United Statesapplication Serial No. 710,781, assigned tov the same assignee asthe present application. I A an arrangement is disclosed in which positional information, as for example azimuth data, may be transmitted by a plurality of pulse of the same polarity and of uniform amplitude, As is discussed, such a teledata-system is especially useful in connection with radio detection and ranging or radar systems, in which the indicator is located at a point remote from the'scanner. In such an arrangement, azimuth data must be transmitted in addition to 'the usual radar video and radar trigger signals. By employing the teachings of the present application in combination with those of the above-mentioned prior application, all the necessary information may be transmitted over a single communication channel, which may or may not include a radio link.

In the operation of such a combined system. it is highly desirable that one of the three groups of signals, namely the azimuth data signals, shall be given precedence over the other two groups of signals. namelv the radar video and radar trigger signals. The present invention provides an arrangement for accomplishing this, which is simpler and more satisfactory than previously known arrangements.

An object of the present invention is to provide combining and separating circuits which are adapted for receiving a plurality of signals, transmitting them over a single channel, and reproducing them at a remote point with their individuality preserved.

A further object of the present invention is to provide combining and separating circuits which give precedence to a chosen one of a plurality of input signa s, in conveying the several signals to a remote point.

An additional obiect of the present invention is to provide combining and separating circuits which are especially adapted for transmitting radar video, radar trigger and azimuth data signals over a single channel without confusion thereof.

In this prior application,

-. Still another object of theypresent invention is to provide combiningaand separating circuits adaptedfor-receiving radar video, radar trigger and. azimuth data signals, and forreproducing, these-signals at aremote point, precedence inggiven to the azimuth data signals.

Another object'of the-present invention is to provide an improved means for measuring the amplitude of'short-duration pulses.

The mixing circuit in accordance with the invention comprises a plurality of vacuum tubes each having a cathode, an anode and a control electrode. -Means are provided for impressing one of a plurality of input signals upon each of the control electrodes with respect to ground. The anode of afirst of the vacuum tubes is coupled to the cathode of a second of the vacuum tubes. In this way, the first and second oi. the input signals are combined to provide a first composite signal. An additional vacuum tube having a cathode, an anode and a control electrode is provided, and there is a coupling between the anode of the third vacuum tube and the anode of this additional vacuum tube. A coupling is also provided between the anode of the second vacuum tube and the control electrode of the additional vacuum tube. By this arrangement, the first composite signal is combined with the third of the input signals to provide a second composite signal. It is this second composite signal which comprises the output of the combining or mixing circuit, and this output may be transmitted by means of a radio or wire or other type of link to the separating circuit at a remote point.

The separating circuit in accordance with the present invention comprises a. plurality of vacuum tubes each having a cathode, an anode and a control electrode. A composite wave, as for example the output wave of the above-described mixing circuit, is applied to the control electrode of a first of these vacuum tubes with respect to ground. This composite wave comprises a plurality of signals. A coupling is provided between the anode of the first vacuum tube and the control electrode of a second of the vacuum tubes. A first of the plurality of input signals i developed in the anode circuit of this second vacuum tube. A second of the plurality of input signals appears in the cathode circuit of the first vacuum tube. A coupling is provided between the cathode of the first vacuum tube and the control electrode of a third of the vacuum tubes. Means are coupled to the anode of the third vacuum 3 tube for utilizing a third of the plurality of input signals.

In accordance with an important feature of the present invention, the latter means may comprise a cathode follower having an output circult, and a feedback loop between this output circuit and the control electrode of the third vacuum tube may be provided, in order to maintain substantially constant the average amplitude of the third of the plurality of signals appearing across the output circuit of the cathode follower. This feedback loop may comprise a multivibrator having a triggering terminal and an output terminal. The triggering terminal may be coupled to the output circuit of the oathode follower and the output terminal of the multivibrator may be connected to a capacitor which is also Included in circuit between the control electrode of the third vacuum tube and ground. In a preferred embodiment of the invention, the multivibrator is of the one-shot type.

By connecting a voltmeter or other suitable indicator across the above-mentioned capacitor, there is provided, in accordance with the present invent on, means for accuratelv measuring the am litude of short-d ration ulses ap lied to the control electrode of the third vacuum tube.

The invention in another of its as ects relates to novel features of the instr mental ties described herein for achieving the principal objects of the invention and to novel principles employed in those instrumentalities, whether or not these features and princi les are used for the above princi al objects or in the stated field.

The above and other obiects and features of the invention will be better understood by reference to the following descri tion taken in connection with the accom anving drawings, in which like components are designated by like reference numerals and in which:

Fig. 1 is a schematic circuit diagram of the si nal-combining arran ements in accordance with the present invention;

Fi 2 shows ra hicallv a composite wave appearing at the out ut of the circuit of Fig. 1: and

Fi 3 is a schematic circuit diagram of the si nal-separating arrangements in accordance with the resent invention.

Referring to Fig. 1, there is shown a video am lifier comprising a first vacuum tube I, the control electrode 2 of which is coupled by means of a capacitor 3 to the movable arm or slider 4 of a potentiometer 5 which in turn is connected between video si nal input terminals 5 and I. A resistor 8 is connected between control electrode 2 and ground. Cathode 3 of vacuum tube I is grounded through resistor I3. Screen-grid II is connected to a source of suitable positive potential dia rammatically illustrated at I2, and sup ressor-grid I3 is grounded.

The anode ll of vacuum tube I is connected through a resi tor I5 and an inductor I6 to a source of suitable positive potential indicated at IT. Anode I4 is also coupled, by means of capacitor l8, to the control electrode i9 of second vacuum tube 20. A resistor 2| is connected between control electrode is and ground.

Cathode 22 of vacuum tube 20 is grounded through a resistor 23 shunted by a capacitor 24. The screen-grid 25 of vacuum tube 20 is connected to positive source I2, and the suppressorgrid 23 is grounded.

The anode 21 of vacuum tube 20 is connected through a resistor 23 and an inductor 29 to positive potential source I'I. Anode 21 is also coupled.

'4 by a capacitor 30, to the control electrode 3| oi a vacuum tube 32. Control electrode II is connected through resistor 33 to the junction of series-connected resistors 34 and 35, which are connected as a voltage divider between potential source II and ground.

The cathode 36 of vacuum tube 32 is connected ,to ground through a potentiometer 21, the movable arm 38 of which is connected to an output terminal 39, the other output terminal 40 being grounded. The screen-grid ll and the anode 42 of vacuum tube 32 are both connected to potential source II. The suppressor-grid 43 of vacuum tube 32 is grounded.

Vacuum tube 44 has its cathode 5 connected to cathode 36 of vacuum tube 32. The control electrode 46 of vacuum tube 44 is connected to the movable arm 41 of a potentiometer 43, which in turn is connected in series with a resistor l3 between source I1 and ground. A capacitor 5. is connected between control electrode 43 and ground. The screen-grid 5i of vacuum tube N is connected to source II, as is anode 52. The suppressor-grid 53 of vacuum tube 44 is grounded.

For the purpose of introducing trigger signals, a pair of terminals 54 and 55 are provided. the latter terminal being grounded. Terminal 54 is coupled by a capacitor 56 to the control electrode 51 of the left-hand portion of vacuum tube 53. A resistor 59 is connected between control electrode 51 and ground. The cathode 63 is grounded. The anode 6| is connected through a resistor 62 to source I l, and is coupled by a capacitor 63 to the cathode 64 of the right-hand portion of vacuum tube 58. Cathode 54 is connected to ground by a resistor 65. The control electrode 66 and the anode 51 of the right-hand portion of vacuum tube 58 are connected together and to cathode 9 of vacuum tube I.

A pair of terminals 68 and 69 are provided for the purpose of introducing the azimuth signal input, terminal 69 being grounded. Terminal 63 is coupled by a capacitor 10 to the control electrode II of a vacuum tube 12, control electrode II being connected by a resistor I3 to a source of suitable negative potential indicated at I4. The cathode I5 is grounded, as is the suppressorgrid Hi. The screen-grid I1 is connected to source I I. The anode I8 is connected through a resistor 19 to anode 21 of vacuum tube 20.

In operation, the positive video signals which are applied to input terminals 5 and I are amplified by vacuum tubes I and 20, the extent of this amplification being controllable by the setting of potentiometer 5. Inductors l5 and 23 in the anode circuits respectively of vacuum tubes I and 20 serve as peaking choke cofls.

The positive trigger signals are applied to terminals 54 and 55 and are shaped by vacuum tube 58. The positive trigger signal voltages charge capacitor 56, and this charge leaks oif exponentially through resistor 59. Thus a trigger pulse having a steep leading edge and a sloped trailing edge is developed across resistor 52 and applied to diode cathode 64 by means of capacitor 53. If desired, capacitor 63 may be made adjustable and used as a trigger signal gain control. The output of the trigger shaping circuit, which may for example comprise pulses having an amplitude of 40 volts, is mixed addltively with the radar video signals in view of the connection from the diode anode (electrodes 68 and 61) to cathode 9 of vacuum tube I. The right-hand portion of vacuum tube 58 serves as a diode rectifier to prevent any negative radar video signals,

which may be developed across resistor I0, from i'eeding back through the trigger shaping circuit.

The azimuth signal input is applied to terminals 68 and 69, and may comprise 150-volt positive pulses. Vacuum tube 12 is normally biased far below cut-oil, since its control electrode H is connected to negative potential source having for example, a potential of 105 volts. When the positive azimuth pulses are applied through capacitor 10 to control electrode 1|, however, vacuum tube 12 becomes conductive and a large current flows through resistors 28 and 19 in its anode circuit. Since resistor 28 is common to the anode circuits of vacuum tubes 12 and 80, this large current flow through vacuum tube 12 causes anode 21 of vacuum tube to change its potential with respect to ground in a negative direction. Its potential may, for example, become less positive by ap roximately 100 volts during each azimuth signal pulse.

The composite signal wave at the output of tube 20 is fed. by means of capacitor 30, to vacuum tube 32, which is arran ed to operate as a cathode follower. Cathode 36 of this vacuum tube is normally positive with respect to ground, as for example by volts. Since the azimuth pulses always cause at least 60-volt negative excursions of anode 21, even when the radar trigger and azimuth pulses .are coincident, the azimuth pulses will drive control electrode 0! sufiiciently negative with res ect to cathode 06 to cut oil vacuum tube 32. In this manner, the azimuth pulses take precedence over the video or trig er signals.

The out ut of cathode follower vacuum tube 02 is developed across potentiometer 31, and a desired portion of it is chosen by the setting of movable arm 38 and appears between output terminals 39 and 40.

Vacuum tube 44 serves as a clipper, and has pled by means of capacitor II1 to the control- A electrode H8 of a vacuum tube H9. The resistor I20 is connected between control and ground.

The cathode electrode I II I2I of vacuum tube H9 is grounded. The screen-grid I 22" is connected to the junction of resistors I23 and I24 connected in series between positive potential source I1 and ground, and this electrode is by-passed to ground by a capacitor I25. The suppressor-grid I26 is grounded. The anode I21 is connected to an azimuth signal output terminal I28, the other azimuth signal output terminal I29 being grounded.

Cathode I08 of vacuum tube I05 is coupled by a capacitor I30 to the control electrode I 3I of a vacuum tube I32. Resistors I33 and I34 are connected in series between control electrode I3I and negative potential source 14.

The cathode I35 of vacuum tube I32 is grounded. as is the suppressor-grid I36. The screengrid I31 is connected to positive potential source I1. The anode I38 is connected to source I1 through a resistor I39, and is coupled by a capacitor I40 to the control electrode I 4| of a vacuum tube I42. A resistor I43 is connected between control electrode I4I and ground. The cathode I44 is grounded, as is the suppressorgrid I45. Screen-grid I46 is connected by a reits control electrode 46 maintained at a desired positive potential relative to ground depending upon the setting of sliding arm 41 of potentlometer 48. Bv suitably adjusting this positive potential. the extent of the negative excursions oi cathode due to the azimuth pulses may be limited to a desired value. Thus potentiometer 08 serves as an azimuth gain control.

The com osite wavea pearin at terminals 39 and 40 is illustrated in Fig. 2. It is seen to comprise positive radar video signals 80, ne ative azimuth pulses 8|, and positive radar trigger signals 82. The relative amplitudes of these si nals de ends, of course. upon the settings of potentiometers 31 and 48, and upon the value of capacitor 63.

The composite output wave may be used to modulate a radio transmitter, or it may be sent directly to the receiving point by a suitable wire line or other conductive connection. Such intermediate link is not a part of the present invention.

Referring now to Fig. 3, which is a schematic circuit diagram of the signal-separating arrangements of the present invention, there is shown a video amplifier I00 having input terminals WI and I02, the latter terminal being grounded. The un rounded output terminal of video amplifier I00 is coupled by means of a capacitor I00 to the control electrode I04 of a vacuum tube I06. Control electrode I04 is connected by means of a resistor I06 to a source of negative potential I01 having, for example, a, potential of three volts.

sistor I41 to the junction of a resistor I48 and a capacitor I49 connected in series between potential source I1 and ground. The anode I50 is connected through an inductor I5I and a resistor I52 to the junction of resistors I41 and I48.

Anode I50-is coupled by a capacitor I53 to the control electrode I54 of the left-hand portion of a vacuum tube I55, a resistor I56 being connected between this control electrode and ground. The anode I 51 is connected to positive potential source I1.

The cathode I58 oi the left-hand portion of vacuum tube I is connected to ground through a resistor I59 and is coupled by a capacitor I60 to the control electrode I6I of a thyratron I62. Control electrode I6I is connected by a resistor I63 to the movable armof a potentiometer I64, which in turn is connected in series with a resistor I65 between round and negative potential source 14. The cathode I66 of thyratron I62 is connected to ground through a resistor I61, and is directly connected to a trigger signal output terminal I68, the other trigger signal output terminal I69 being grounded. The anode I10 of thyratron I62 is connected through a resistor Hi to positive potential source I1. A series network comprising a resistor I12 and a capacitor I13 is connected between anode I10 and ground.

Cathode I58 of the left-hand portion of vacuum tube I55 is also cou led by a capacitor I14 to the control electrode Iliof the right-hand portion of vacuum tube I55. ontrol electrode I15 is connected to the junction of resistors I16 and I 11 which are in turn connected in series between ground and negative potential source 14. The cathode I96 is grounded.

The anode I18 of the right-hand portion of vacuum tube I55 is connected through a resistor I19 to positive potential source I1, and is coupled by a capacitor I80 to the control electrode I8I of the left-hand portion of a vacuum tube I82. A resistor I03 is connected between control electrode III and ground. The cathode I84 is grounded. The anode I85 is connected through a resistor I06 to positive potential source I1, and is also connected by a resistor I01 shunted by a capacitor I08 to the control electrode I89 of the right-hand portion of vacuum tube I82.

Control electrode I09 is connected by a resistor I80 to negative potential source 14. The cathode I9I is grounded. The anode I92 is connected to the junction of resistor I19 and capacitor I60. This junction is also connected by a resistor I93 to the junction of resistors I33 and I34, the latter junction being by-passed to ground by a capacitor I94. A voltmeter I95 may be connected between ground and the junction of resistors I33 and I34, as shown.

In operation, the input signal which is applied to terminals IM and I02 comprises a composite wave having the general characteristics shown in Fig. 2. Since video amplifier I is assumed to have an even number of stages, a, similar composite wave is applied to control electrode I04 of vacuum I05. This vacuum tube operates as a cathode follower, and its control electrode I04 has applied to it a suitable negative bias potential, as for example three volts. This bias serves to limit the azimuth pulses to a desired value, as for example 11 volts. The video signal output appears across resistor II2 in the cathode circuit of vacuum tube I05 and may be utilized at terminals H0 and III.

Resistor H6 in the anode circuit of vacuum tube I05 has no appreciable efiect upon the operation of this tube as a cathode follower since, the

tube being a pentode, its anode current is determined largely by the potential applied to screengrid I I3. The negative azimuth pulses from video amplifier I00, however, cause the anode current of vacuum tube I05 to be cut off, thus producing positive excursions of anode II5 which may, for example, have a magnitude of approximately 20 volts. These positive anode excursions are applied to control electrode I I8 of vacuum tube I I9, which is so negatively biased by grid rectification action in the circuit of elements H1, H8 and I20 as to respond only to positive excursions. Such signals render the tube conductive, causing the azimuth pulse output to be developed between terminals I28 and I29.

The output of vacuum tube I05, as developed across its cathode resistors I09 and I I2, is applied to control electrode I3I of vacuum tube I32, which functions as a tri ger signal separator. Control electrode I3I is normally biased to a substantial negative value, as for example approximately 40 volts. This bias is suflicient to cut oif the tube for peak values of the radar video signal. The azimuth signal pulses are of negative polarity and hence have no effect upon vacuum tube I32. The trigger signal pulses are positive and have approximately double the amplitude of the peak radar video signals. Thus each trigger pulse overcomes the normal negative bias on control electrode Ill and renders vacuum tube I32 conductive for the brief duration of each pulse.

The resultant negative anode swings are amplifled by vacuum tube I42, which operates with zero bias on its control electrode I. The purpose of series screen resistor I41 is to reduce the anode current of this vacuum tube to a reasonable value. Each negative trigger pulse from vacuum tube I32 causes the anode current of vacuum tube I42 to be cut oil. Inductor I5I in the anode circuit or this tube sharpens the resultant positive trigger pulses developed at anode I50. These pulses, which may for example have an amplitude of between 50 and 60 volts, are applied to control electrode I54 of the left-hand portion of vacuum tube I55, this tube portion functioning as a cathode follower and serving to provide an impedance step-down.

The positive trigger pulses developed across resistor I59 are applied to control electrode IN 01 thyratron I62. This electrode is negatively biased by an amount depending upon the setting of potentiometer I64, so that the trigger pulses must exceed this bias potential in order to tire thyratron I62. Thus potentiometer I64 serves as a trigger sensitivity control. Resistor I12 limits the current flow through thyratron I62. The trigger pulses developed across resistor I61 may be utilized at trigger output terminals I68 and I69. These pulses for example may have a duration of l microsecond at 70 volts and one ampere.

For the purpose of maintaining the positive trigger pulses applied to control electrode I6I o1 thyratron I62 at a substantially constant level, a feedback loop is provided. The positive pulses developed across cathode resistor I59 associated with vacuum tube I55 are applied by means of capacitor I14 to control electrode I15 of the right-hand portion of vacuum tube I55. This electrode is normally held at a substantially negative potential, as for example approximately 66 volts, by the voltage divider comprising resistors I16 and I11. The right-hand portion of vacuum tube I 55 conducts on each positive trigger pulse which exceeds this bias potential, and the resultant negative voltage swings of anode I18 are employed to trigger a one-shot multivibrator comprising vacuum tube I82. The lefthand portion of this vacuum tube is normally conducting so that its anode I65 has approximately the same potential as its control electrode I8I. The right-hand portion of vacuum tube I82 is normally non-conducting.

When negative trigger pulses are received from vacuum tube I55, control electrode I8I is rendered increasingly negative so that the left-hand portion of vacuum tube I82 is cut oil. The resultant positive swings of anode I85 are fed through resistor I81 shunted by capacitor I88 to control electrode I99 of the right-hand portion of vacuum tube I82, thereby rendering this electrode less negative and causing the right-hand portion of the tube to become conductive. Anode I92 thereupon becomes decreasingly positive, and this negative voltage swing is applied through an integrating network comprising resistors I93 and I34 and capacitor I94 to control electrode I3I of vacuum tube I32. Capacitor I94 is normally charged so that its ungrounded terminal is substantially negative with respect to ground, as for example by 40 volts. The negative voltage swings of anode I92 increase the negative voltage on capacitor I94 and thus increase the negative bias which is applied to control electrode I3I of vacuum tube I32.

Capacitor I94 is charged negatively at a slow exponential rate. This gradually increases the negative bias voltage on control electrode I3I of vacuum tube I32 until the pulse amplitude developed across cathode resistor I59 associated with vacuum tube I55 is reduced to a desired value, as for example to less than 50 to 60 volts. when this condition is reached, the multivibrator comprising vacuum tube I82 rests until it is triggered by another pulse from anode I18 of vacuum tube I55. The charge and discharge of capacitor I94 occurs at a rate faster than the amplitude variation of the radar trigger pulses, but less rapidly than the pulse repetition rate. In this manner, the average pulse amplitude delivered at output terminals I68 and I89 remains essentially constant for a wide range of amplitudes for the input pulses applied by capacitor I80 to vacuum tube I32. The small departure from the average in the amplitude of individual pulses applied to control electrode l6l of thyratron I62, due to hunting action of the feedback circuit, is well within the firing range of the tube and hence introduces no difliculty.

As pointed out above, the negative charge on capacitor I94 increases as a function of the amplitude of the trigger signal pulses applied by capacitor I30 to control electrode I3l of vacuum tube I32. Although these input pulses are of extremely short duration, it is evident that the voltage across capacitor I94, as indicated for example by voltmeter I95, is closely proportional to the amplitude of the input pulses. This portion of the circuit, therefore, constitutes a very satisfactory means for measuring the amplitude of short-duration pulses, a measurement which has been difllcult to make with previously known circuit arrangements.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A separating circuit comprising: a plurality of vacuum tubes, each having a cathode, an anode, and a control electrode; means for applying a, composite wave comprising a plurality of signals upon the control electrode of a first of said vacuum tubes with respect to ground; a coupling between the anode (go said first vacuum tube and the control electrode of a second of said vacuum tubes; means in the anode circuit of said second vacuum tube for utilizing a first of said signals; means in the cathode circuit of said first vacuum tube for utilizing a second of said signals; a coupling between the cathode of said first vacuum tube and the control electrode of a third of said vacuum tubes; means coupled to the anode of said third vacuum tube for utilizing a third of said signals, said means comprising a cathode follower having an output circuit; and means including a feedback loop between said output circuit and the control electrode of said third vacuum tube for maintaining the average amplitude of the third of said signals appearing across said output circuit substantially constant.

2. A separating circuit comprising: a plurality of vacuum tubes, each having a cathode, an anode, and a control electrode; means for applying a composite wave comprising a plurality of signals upon the control electrode of a first of said vacuum tubes with respect to ground; a coupling between the anode of said first vacuum tube and the control electrode of a second of said vacuum tubes; means in the anode circuit of said second vacuum tube for utilizing a first of said signals; means in the cathode circuit of said first vacuum tube for utilizing a second of said signals; a coupling between the cathode of said first vacuum tube and the control electrode of a third of said vacuum tubes: means coupled tothe anode of said third vacuum tube forutilizing a third of said signals, said means comprising a cathode follower having an output circuit; and a feedback loop between said output circuit and the control electrode of said third vacuum tube, said feedback loop comprising a single-stability multivibrator.

3. A regulated amplifier for providing output pulses of substantially constant amplitude from an input signal comprising pulses of widely varying amplitude, comprising: a vacuum tube having a cathode, an anode, and a control electrode; means for impressing said input signal between said control electrode and ground; a cathode follower having input and output electrodes, said input electrode being coupled to the output electrode of said vacuum tube; singlestability multivibrator having a triggering terminal and an output terminal; a coupling between said output electrode and said triggering terminal; a capacitor connected between said output terminal and ground; and a connection between said control electrode and the ungrounded terminal of said capacitor.

4. A regulated amplifier for providing output pulses of substantially constant amplitude from an input signal comprising pulses of widely varying amplitude, comprising: a vacuum tube having a cathode, an anode, and a control electrode; means for impressing said input signal between said control electrode and ground; a cathode follower having input and ,output electrodes, said input electrode being coupled to the output electrode of said vacuum tube; a multivibrator having a triggering terminal and an output terminal, said multivibrator being of the single-stability type; a coupling between said output electrode and said triggering terminal; a capacitor connected between said output terminal and ground; and a connection between said control electrode and the ungrounded terminal of said capacitor.

5. In combination, a composite wave sending system and a receiving system therefor, the sending system comprising: a first amplifier tube circuit receiving positive trigger pulses in its grid input circuit and producing amplified negative pulses in its plate output circuit, a second amplifying tube circuit receiving video input signals in its grid input circuit and producing an amplified and inverted version thereof in its plate output circuit, a rectifier coupling the plate output circuit of said first tube to the oathode of the second tube for causing high amplitude negative pulse voltage excursions of the plate voltage of said second tube greatly exceeding in magnitude the amplified versions of the video grid input voltage thereof, a third amplifier tube circuit receiving high amplitude positive pulses in its grid input .circuit and producing high amplitude negative pulses in its plate circuit, and a fourth amplifier tube circuit having its plate coupled to the plate of said third tube and its grid input circuit coupled to the plate of the second tube, the fourth tube producing low amplitude positive output voltage variations corresponding to the positive video voltage variations in the input circuit of the second tube and also producing high amplitude positive pulses corresponding to the input pulses of the first tube, and these output components '11 being combined in the intercoupled plate circuits of the third and fourth tubes with the high amplitude negative pulses produced through the operation of the third tube; and said receiving system comprising: a first separator circuit tube having a control grid receiving a version of the composite wave of high amplitude positive trigger pulses, low amplitude video voltage variations, and high amplitude negative pulses, said first separator circuit tube having a cathode load output circuit and a plate output circuit, the plate output circuit supplying limited-amplitude sharp positive voltage excursions corresponding to the input'of the third tube in the composite wave sending system and the cathode output circuit supplying sharp high amplitude positive voltage pulses corresponding to the trigger pulse input of the first tube in the composite wave sending system and also low amplitude video voltage variations, a second amplifier tube with its grid coupled to the plate circuit of said first separator circuit tube through a resistancecapacitance bias storage and coupling circuit providing a negative grid bias voltage to said second tube resulting from grid-rectification therein and limiting the output of the second tube to brief negative pulses corresponding only to the output of the third tube in the composite wave sending system, a third separator circuit tube having its grid circuit coupled to the cathode circuit of the first separator circuit tube, means supplying high voltage negative bias to the grid circuit of said third separator circuit tube, this voltage exceeding the sum of the cut oil bias of this tube and the positive peak values of the video voltage supplied through the cathode circuit of the first separator circuit tube whereby only the very high amplitude positive trigger pulses in the cathode circuit of said first separator circuit tube are suflicient to produce such changes of grid voltage in said third separator circuit tube as to produce plate current pulses therein, a two-stage amplifier coupled to the plate circuit of the third separator circuit tube, the output stage of the two-stage amplifier being a cathode follower stage for producing output voltage variations in the same sense as the input voltage variations in the input circuit of the third separator circuit tube, and hence for producing positive high amplitude pulses corresponding to the positive trigger pulses, a thyratron having a control grid coupled to the cathode follower output circuit of said two-stage amplifier to be fired recurrently by said amplified positive trigger pulses, the output circuit of the thyratron providing high power control current pulses timedaccording to said trigger pulses, and a feedback loop circuit between the output circuit of the two-stage amplifier and the grid bias circuit of said third separator circuit tube, said feedback loop circuit comprising a one-shot multivibrator including a normally conductive input tube portion with a grid circuit coupled to the output circuit of said two-stage amplifier and a normally non-conductive output tube circuit with its anode circuit coupled to the grid circuit of said third separator circuit tube, cross couplings being provided between the control grids and the anodes of the two tuba of the multivibrator, and a capacitor integrator connected in the output circuit of said multivibrator and the grid circuit of said third separator circuit tube for receiving current impulses from the output tube of said multivibrator corresponding to its periods of conductivity and supplementing the negative bias normally supplied to the control.

grid circuit of said third separator circuit tube by an amount variable automatically to suppress changes of output amplitude of said two-stage amplifier.

6. A composite wave sending system comprising a first amplifier tube circuit receiving positive trigger pulses in its grid input circuit and producing amplified negative pulses in its plate output circuit, a second amplifier tube circuit receiving video input signals in its grid input circuit and producing an amplified and inverted version thereof in its plate output circuit, means connected between the plate output circuit of said first tube and the cathode of the second tube for causing high amplitude negative pulse voltage excursions of the plate voltage of said second tube greatly exceeding in magnitude the amplified versions of the video grid input voltage thereof, a third amplifier tube circuit receiving high amplitude positive pulses in its grid input circuit and producing high amplitude negative pulses in its plate circuit, and a fourth amplifier tube circuit having its plate coupled to the plate of said third tube and its grid input circuit coupled to the plate of said second tube, the fourth tube producing low amplitude positive output voltage variations corresponding to the positive video voltage variations in the input circuit'of the second tube and also producing high amplitude positive pulses corresponding to the input pulses of the first tube, these output components being combined in the intercoupled plate circuits of the third and fourth tubes with the high amplitude negative pulses produced by the third tube.

7. A composite wave sending system comprising a first amplifier tube circuit receiving positive trigger pulses in its grid input circuit and producing amplified negative pulses in its plate output circuit, a second amplifier tube circuit receiving input video signals in its grid input circuit and producing an amplified and inverted version thereof in its plate output circuit, means including a rectifier coupling the plate output circuit of said first tube to the .cathode of the second tube for causing high amplitude negative pulse voltage excursions of the plate voltage of said second tube greatly exceeding in magnitude the amplified versions of the video grid input voltage thereof, a third amplifier tube circuit receiving high amplitude positive pulses in its grid input circuit and producing high amplitude negative pulses in its plate circuit, and a fourth amplifier tube circuit having its plate coupled to the plate of said third tube and its grid input circuit coupled to the plate of the second tube, the fourth tube producing low amplitud positive output voltage variations corresponding to the positive video voltage variations in the input circuit of the second tube and also producing high amplitude positive pulses corresponding to the input pulses of the first tube, these output components being combined in the intercoupled plate circuits of the third and fourth tubes with the high amplitude negative pulses produced through the operation of the third tube.

8. Apparatus for combining three input signals to provide a composite transmission wave and for receiving said composite wave and separating it into three output signals respectively corresponding to said three input signals, the first and third input signals being distinct pulse tive ones of said input signals upon the respective ones of said three vacuum tubes; means including a coupling between said first and second vacuum tubes for combining versions of the first and second of said input signals into a first composite signal with negative polarity high voltage pulses; a fourth vacuum tube; means including a coupling between the output circuits of said third vacuum tube and said fourth vacuum tube and a coupling between the output circuit of said second vacuum tube and the input circuit of said fourth vacuum tube for combining a version of said first composite signal with a version of said third input signal to provide the composite transmission wave; three separator circuit vacuum tubes; means for impressing said composite transmission wave upon a first of said separator circuit vacuum tubes, a coupling between said last-mentioned vacuum tube and a second of said separator circuit vacuum tubes; means associated with said last-mentioned vacuum tube for utilizing the output signals corresponding to the third input signal; means associated with said first separator circuit vacuum tube for utilizing the output signals corresponding to the second input signal; a coupling between said last-mentioned vacuum tube and the third separator circuit vacuum tube; means including an amplifier coupled to said last-mentioned vacuum tube for utilizing a third of said output signals; and means including a single-stability multivibrator and a voltage storage capacitor interposed between said third separator circuit vacuum tube and said amplifier for variably biasing said third separator circuit tube according to the output level of said amplifier, said multivibrator having its input circuit coupled to the output circult of said amplifier and its output circuit connected to said capacitor and to the grid circuit of said third separator circuit vacuum tube.

DAVID E. KENYON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,011,315 Gilbert Aug. 13, 1935 2,132,655 Smith Oct. 11, 1938 2,166,688 Kell July 18, 1939 2,190,743 Vance Feb. 20, 1940 2,192,121 Bedford Feb. 27, 1940 2,207,839 Tolson July 16, 1940 2,224,134 Blumlein Dec. 10, 1940 2,229,964 Dome et al. Jan. 28, 1941 2,233,317 Konkle Feb. 25, 1941 2,249,942 Campbell July 22, 1941 2,266,154 Blumlein Dec. 16, 1941 2,284,714 Bedford June 2, 1942 2,287,334 White June 23, 1942 2,293,148 Kell Aug. 18, 1942 2,297,543 Eberhardt Sept. 29, 1942 2,363,809 Schade Nov. 28, 1944 2,368,351 Ewen Jan. 30, 1945 2,403,521 Gilbert July 9, 1946 2,408,079 Labin et al Sept. 24, 1946 2,415,919 Thomas Feb. 18, 1947 2,418,116 Greig Apr. 1, 1947 2,421,521 Pooh June 3, 1947 2,425,315 Atwood et al. Aug. 12, 1947 FOREIGN PATENTS Number Country Date 476,935 Great Britain Dec. 15, 1937 OTHER REFERENCES Television: The Electronics of Image Transmission, 1940, by Zworykin et al., pp. 464-466. 

